Apparatus for applying optical gradient forces

ABSTRACT

A method and apparatus for control of optical trap arrays and formation of particle arrays. The method and apparatus provides a laser and a time variable diffractive optical element to allow dynamic control of optical trap arrays and consequent control of particle arrays and also the ability to manipulate singular objects using a plurality of optical traps.

[0001] This invention was made with U.S. Government support underContract No. DMR-9320278 awarded by the National Science Foundation,through the MRSEC Program of the National Science Foundation under AwardNo. DMR-9400379, and through a GAANN fellowship from the Department ofEducation. The U.S. Government also has certain rights to the inventionpursuant to funding under contracts NSFDMR-978031 and NSFDMR 980595.

[0002] The present invention is directed generally to a method andapparatus for control of optical traps. More particularly, the inventionis directed to methods and apparati for dynamic control of optical traparrays and for controllably filling an optical trap array withparticles. Such methods and apparati enable the dynamic change ofoptical trap location, the strength and size of each optical trap andenable controlled adaptation and feedback for use of the optical trapsfor investigation and manufacturing purposes.

[0003] It is known to construct optical tweezers using optical gradientforces from a single beam of light to manipulate the position of a smalldielectric particle immersed in a fluid medium whose refractive index issmaller than that of the particle. The optical tweezer technique hasbeen generalized to enable manipulation of reflecting, absorbing and lowdielectric constant particles as well.

[0004] The current conventional systems therefore can manipulate asingle particle by using a single beam of light to generate a singleoptical trap. To manipulate multiple particles with such systems,multiple beams of light must be employed. The difficulty of creatingextended multiple-beam traps using conventional optical tweezermethodology inhibits their use in many potential commercial applicationssuch as the fabrication and manipulation of nanocomposite materialsincluding electronic, photonic and opto-electronic devices, chemicalsensor arrays for use in chemical and biological assays, and holographicand computer storage matrices.

[0005] It is therefore an object of the invention to provide an improvedmethod and system for establishing a plurality of optical traps.

[0006] It is one object of the invention to provide a novel method andapparatus for control of optical traps and small particle arrays.

[0007] It is yet another object of the invention to provide an improvedmethod and apparatus for dynamic control of optical traps.

[0008] It is still a further object of the invention to provide a novelmethod and apparatus for sequential formation of optical traps and/orparticle arrays.

[0009] It is an additional object of the invention to provide animproved method and apparatus to exert dynamic control of size, shapeand strength of optical traps.

[0010] It is yet a further object of the invention to provide a novelmethod and apparatus for computer generation of a holographic patternfor dynamic control of optical trap configurations.

[0011] It is still another object of the invention to provide animproved method and apparatus for applying a spatial light modulator toa laser beam for dynamic control of optical trap arrays.

[0012] It is also an additional object of the invention to provide anovel method and apparatus employing a mechanical device for selectivepassage of laser beams for time varying formation of particular opticaltrap arrays.

[0013] It is still a further object of the invention to provide animproved method and apparatus for enhanced particle flow into opticaltraps and selective output of different particles for optical trapping.

[0014] It is also another object of the invention to provide a newmethod and apparatus for inspection and manipulation of biological mediausing a controlled array of optical traps.

[0015] It is another object of the invention to provide a novel methodand system for using a single beam of light with diffractive optics forforming a configuration of light beams for establishing a plurality ofoptical traps.

[0016] It is an additional object of the invention to provide a novelmethod and apparatus for using holograms for generating an opticalgradient field for controlling a plurality of particles or other opticalmedia.

[0017] It is a further object of the invention to provide an improvedmethod and system for establishing a plurality of optical traps for avariety of commercial applications relating to manipulation of smallparticles such as in photonic circuit manufacturing, nanocompositematerial applications, fabrication of electronic components,opto-electronic devices, chemical and biological sensor arrays, assemblyof holographic data storage matrices, facilitation of combinatorialchemistry applications, promotion of colloidal self-assembly, and themanipulation of biological materials.

[0018] It is still another object of the invention to provide animproved method and system for constructing a temporally and spatiallyvarying configuration of optical gradient fields for commercialapplications.

[0019] It is also an object of the invention to provide a novel methodand system for using one or more laser beams in conjunction with one ormore diffractive optical elements for constructing a selectable timevarying and/or particular spatial array of optical traps formanipulating a dielectric material.

[0020] It is yet a further object of the invention to provide animproved method and system using a single input laser beam, adiffractive optical element, and a diverging and/or converging lens toform a static or dynamic optical trap.

[0021] It is still an additional object of the invention to provide anovel method and system for constructing an optical trap array which isdirectly observable by a user.

[0022] It is also a further object of the invention to provide animproved method and system employing a laser beam input to a diffractiveoptical element with a beam scanning system enabling scanning of anarray of optical traps for various commercial applications.

[0023] It is in addition another object of the invention to provide anovel method and apparatus for constructing an optical trapconfiguration using a laser beam, a diffractive optical element and adiverging or converging optical system to form the trap configuration ata selectable location relative to an objective lens focal plane.

[0024] It is still another object of the invention to provide animproved method and apparatus for using a laser beam and an obliquelypositioned diffractive optical element to filter out any undiffractedbeam for efficient utilization of only a diffracted optical beam inconstructing an optical trap arrangement.

[0025] It is yet another object of the invention to provide a novelmethod and apparatus for using a laser beam input to a diffractiveoptical element to generate at least a two-dimensional arrangement ofoptical traps out of the focal plane of an objective lens.

[0026] It is also yet another object of the invention to provide animproved method and system for employing a light beam and diffractiveoptics in conjunction with a plurality of telescope lenses to scan anoptical trap array.

[0027] It is yet an additional object of the invention to provide anovel method and system for establishing an array of optical traps usinga single light beam input to a diffractive optical element and anoptical system for controllably scanning the optical trap array suchthat small amplitude oscillatory displacements are applied todynamically stiffen the optical traps.

[0028] It is another object of the invention to provide a novel methodfor creating multiple independently steered optical traps using atime-dependent addressable phase-shifting medium (such as a liquidcrystal phase shifting array) as a diffractive optical element.

[0029] It is a further object of the invention to provide a novel methodfor creating time-dependent optical gradient fields for the segregationof microscopic particles.

[0030] It is yet another object of the invention to provide a novelmethod for manipulating a plurality of biological objects including thecrystallization of proteins.

[0031] Other objects, features and advantages of the present inventionwill be readily apparent from the following description of the preferredembodiments thereof, taken in conjunction with the accompanying drawingsdescribed below wherein like elements have like numerals throughout.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032]FIG. 1 illustrates a prior art method and system for a singleoptical tweezer;

[0033]FIG. 2 illustrates a prior art method and system for a single,steerable optical tweezer;

[0034]FIG. 3 illustrates a method and system using a diffractive opticalelement;

[0035]FIG. 4 illustrates another method and system using a tiltedoptical element relative to an input light beam;

[0036]FIG. 5 illustrates a continuously translatable optical tweezer(trap) array using a diffractive optical element;

[0037]FIG. 6 illustrates a method and system for manipulating particlesusing an optical tweezer array while also forming an image for viewingthe optical trap array;

[0038]FIG. 7A illustrates an image of a four by four array of opticaltweezers (traps) using the optical system of FIG. 6; and FIG. 7Billustrates an image of one micrometer diameter silica spheres suspendedin water by the optical tweezers of FIG. 7A immediately after thetrapping illumination has been extinguished, but before the spheres havediffused away;

[0039]FIG. 8 illustrates a holographic optical trap system including amovable knife edge feature;

[0040]FIG. 9A illustrates a 10×10 array of optical traps formed on aglass-water interface; FIG. 9B illustrates optical traps with a focusabout 2 microns above the glass and the fifth row of optical traps isexposed to a flow of particles; FIG. 9C illustrates further filling pfparticles compared to FIG. 9B with filling of the eighth row of theoptical traps and FIG. 9D illustrates a completely filled pattern of theoptical traps; and

[0041]FIG. 10 illustrates an optical trap control system with microscopeimaging.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] In order to best understand the improvement of the invention,FIGS. 1 and 2 illustrate several prior art methods and systems. Thesesystems will first be reviewed, and then the invention will be describedin terms of the preferred embodiment examples of FIGS. 3-7A and 7B. Inprior art optical tweezer system 10 of FIG. 1, optical gradient forcesarise from use of a single beam of light 12 to controllably manipulate asmall dielectric particle 14 dispersed in a medium 16 whose index ofrefraction, n_(m), is smaller than that of the particle 14. The natureof the optical gradient forces is well known, and also it is wellunderstood that the principle has been generalized to allow manipulationof reflecting, absorbing and low dielectric constant particles as well.Any of these techniques can be implemented in the context of theinvention described hereinafter and will be encompassed by use of theterminology optical tweezer, optical trap and optical gradient forcetrap hereinafter.

[0043] The optical tweezer system 10 is applied by using a light beam 12(such as a laser beam) capable of applying the necessary forces neededto carry out the optical trapping effect needed to manipulate aparticle. The objective of a conventional form of the optical tweezer 10is to project one or more shaped beams of light into the center of aback aperture 24 of a converging optical element (such as an objectivelens 20). As noted in FIG. 1 the light beam 12 has a width “w” andhaving an input angle Ø relative to an optical axis 22. The light beam12 is input to a back aperture 24 of the objective lens 20 and outputfrom a front aperture 26 substantially converging to a focal point 28 infocal plane 30 of imaging volume 32 with the focal point 28 coincidingwith an optical trap 33. In general, any focusing optical system canform the basis for the optical tweezer system 10.

[0044] In the case of the light beam 12 being a collimated laser beamand having its axis coincident with the optical axis 22, the light beam12 enters the back aperture 24 of the objective lens 20 and is broughtto a focus in the imaging volume 32 at the center point c of theobjective lens focal plane 30. When the axis of the light beam 12 isdisplaced by the angle Ø with respect to the optical axis 22, beam axis31 and the optical axis 22 coincide at the center point B of the backaperture 12. This displacement enables translation of the optical trapacross the field of view by an amount that depends on the angularmagnification of the objective lens 20. The two variables, angulardisplacement Ø and varying convergence of the light beam 12, can be usedto form the optical trap at selected positions within the imaging volume32. A multiple number of the optical traps 33 can be arranged indifferent locations provided that multiple beams of light 12 are appliedto the back aperture 24 at the different angles Ø and with differingdegrees of collimation.

[0045] In order to carry out optical trapping in three dimensions,optical gradient forces created on the particle to be trapped mustexceed other radiation pressures arising from light scattering andabsorption. In general this necessitates having the wave front of thelight beam 12 to have an appropriate shape at the back aperture 24. Forexample, for a Gaussian TEM₀₀ input laser beam, the beam diameter wshould substantially coincide with the diameter of the back aperture 24.For more general beam profiles (such as Gauss-Laguerre) comparableconditions can be formulated.

[0046] In another prior art system in FIG. 2, the optical tweezer system10 can translate the optical trap 33 across the field of view of theobjective lens 20. A telescope 34 is constructed of lenses L1 and L2which establishes a point A which is optically conjugate to the centerpoint B in the prior art system of FIG. 1. In the system of FIG. 2 thelight beam 12 passing through the point A also passes through the pointB and thus meets the basic requirements for performing as the opticaltweezer system 10. The degree of collimation is preserved by positioningthe lenses L1 and L2 as shown in FIG. 2 to optimize the transferproperties of the telescope 34. In addition, the magnification of thetelescope 34 can be chosen to optimize angular displacement of the lightbeam 12 and its width w in the plane of the back aperture 24 of theobjective lens 20. As stated hereinbefore, in general several of thelight beams 12 can be used to form several associated optical traps.Such multiple beams 12 can be created from multiple independent inputbeams or from a single beam manipulated by conventional reflectiveand/or refractive optical elements.

[0047] In one preferred embodiment of the invention shown in FIG. 3,arbitrary arrays of optical traps can be formed. A diffractive opticalelement 40 is disposed substantially in a plane 42 conjugate to backaperture 24 of the objective lens 20. Note that only a single diffractedoutput beam 44 is shown for clarity, but it should be understood that aplurality of such beams 44 can be created by the diffractive opticalelement 40. The input light beam 12 incident on the diffractive opticalelement 40 is split into a pattern of the output beam 44 characteristicof the nature of the diffractive optical element 40, each of whichemanates from the point A. Thus the output beams 44 also pass throughthe point B as a consequence of the downstream optical elementsdescribed hereinbefore.

[0048] The diffractive optical element 40 of FIG. 3 is shown as beingnormal to the input light beam 12, but many other arrangements arepossible. For example, in FIG. 4 the light beam 12 arrives at an obliqueangle β relative to the optic axis 22 and not at a normal to thediffractive optical element 40. In this embodiment, the diffracted beams44 emanating from point A will form optical traps 50 in focal plane 52of the imaging volume 32 (seen best in FIG. 1). In this arrangement ofthe optical tweezer system 10 an undiffracted portion 54 of the inputlight beam 12 can be removed from the optical tweezer system 10. Thisconfiguration thus enables processing less background light and improvesefficiency and effectiveness of forming optical traps.

[0049] The diffractive optical element 40 can include computer generatedholograms which split the input light beam 12 into a preselected desiredpattern. Combining such holograms with the remainder of the opticalelements in FIGS. 3 and 4 enables creation of arbitrary arrays in whichthe diffractive optical element 40 is used to shape the wavefront ofeach diffracted beam independently. Therefore, the optical traps 50 canbe disposed not only in the focal plane 52 of the objective lens 20, butalso out of the focal plane 52 to form a three-dimensional arrangementof the optical traps 50.

[0050] In the optical tweezer system 10 of FIGS. 3 and 4, also includedis a focusing optical element, such as the objective lens 20 (or otherlike functionally equivalent optical device, such as a Fresnel lens) toconverge the diffracted beam 44 to form the optical traps 50. Further,the telescope 34, or other equivalent transfer optics, creates a point Aconjugate to the center point B of the previous back aperture 24. Thediffractive optical element 40 is placed in a plane containing point A.

[0051] In another form of the invention, arbitrary arrays of the opticaltraps 50 can be created without use of the telescope 34. In such anembodiment the diffractive optical element 40 can be placed directly inthe plane containing point B.

[0052] In the optical tweezer system 10 either static or time dependentdiffractive optical elements 40 can be used. For a dynamic, or timedependent version, one can create time changing arrays of the opticaltraps 50 which can be part of a system utilizing such a feature. Inaddition, these dynamic optical elements 40 can be used to actively moveparticles and matrix media relative to one another. For example, thediffractive optical element 40 can be a liquid crystal phase arrayundergoing changes imprinted with computer-generated holographicpatterns.

[0053] In another embodiment illustrated in FIG. 5, a system can beconstructed to carry out continuous translation of the optical tweezertrap 50. A gimbal mounted mirror 60 is placed with its center ofrotation at point A. The light beam 12 is incident on the surface of themirror 60 and has its axis passing through point A and will be projectedto the back aperture 24. Tilting of the mirror 60 causes a change of theangle of incidence of the light beam 12 relative to the mirror 60, andthis feature can be used to translate the resulting optical trap 50. Asecond telescope 62 is formed from lenses L3 and L4 which creates apoint A′ which is conjugate to point A. The diffractive optical element40 placed at point A′ now creates a pattern of diffracted beams 64, eachof which passes through point A to form one of the tweezer traps 50 inan array of the optical tweezers system 10.

[0054] In operation of the embodiment of FIG. 5, the mirror 60translates the entire tweezer array as a unit. This methodology isuseful for precisely aligning the optical tweezer array with astationary substrate to dynamically stiffen the optical trap 50 throughsmall-amplitude rapid oscillatory displacements, as well as for anyapplication requiring a general translation capability.

[0055] The array of the optical traps 50 also can be translatedvertically relative to the sample stage (not shown) by moving the samplestage or by adjusting the telescope 34. In addition, the optical tweezerarray can also be translated laterally relative to the sample by movingthe sample stage. This feature would be particularly useful for largescale movement beyond the range of the objective lens field of view.

[0056] In another form of the invention shown in FIG. 6 the opticalsystem is arranged to permit viewing images of particles trapped by theoptical tweezers 10. A dichroic beamsplitter 70, or other equivalentoptical beamsplitter, is inserted between the objective lens 20 and theoptical train of the optical tweezer system 10. In the illustratedembodiment the beamsplitter 70 selectively reflects the wavelength oflight used to form the optical tweezer array and transmits otherwavelengths. Thus, the light beam 12 used to form the optical traps 50is transmitted to the back aperture 24 with high efficiency while lightbeam 66 used to form images can pass through to imaging optics (notshown).

[0057] An illustration of an application of the invention is shown inFIGS. 7A and 7B. The diffractive optical element 40 is designed tointeract with the single light beam 12 to create a 4×4 array ofcollimated beams. A 100 mW frequency doubled diode-pumped Nd:YAG laseroperating at 532 nm provides a Gaussian TEM₀₀ form for the light beam12. In FIG. 7A the field of view is illuminated in part by laser lightbackscattered by sixteen silica spheres trapped in the array's sixteenprimary optical tweezers 10. The 1 μm diameter spheres are dispersed inwater and placed in a sample volume between a glass microscope slide anda 170 μm thick glass coverslip. The tweezer array is projected upwardthrough the coverslip and is positioned in a plane 8 μm above thecoverslip and more than 20 μm below the upper microscope slide. Thesilica spheres are stably trapped in three-dimensions in each of thesixteen optical tweezers 10.

[0058] In FIG. 7B is shown the optically-organized arrangement ofspheres {fraction (1/30)} second after the optical tweezers 10 (traps)were extinguished but before the spheres had time to diffuse away fromthe trap site.

[0059] Adaptive Tweezer Mode

[0060] In other forms of the invention the basic optical trap embodimentdescribed hereinbefore can be used in various useful methodologies.Furthermore, other embodiments include apparati and systems which can beconstructed to apply these methods to enhance operation and use of theoptical traps. In particular, the optical traps can be controlled andmodified, and various embodiments employing these features are describedhereinafter.

[0061] A variety of new uses and applications of optical traps can arisefrom time varying construction and dynamic change of optical trapconfiguration. In one form of the invention an array of optical trapscan be advantageously manipulated in the manner shown in FIG. 8. Inoptical system 100, diffractive optical element 102 splits collimatedlaser beam 104 into several (two or more) laser beams 106 and 108. Eachof the several laser beams 106 and 108 are transferred into a separateoptical trap in an object plane 118. Each of these several laser beams106, 108 are transferred to back aperture 110 of the objective lens 112by action of a conventional optical arrangement, such as the telescopeformed by lenses 114 and 116. The objective lens 112 focuses each ofthese several beams 106, 108 into a separate optical trap 132 in theobject plane 118. In a preferred form of the invention a knife edge 120is disposed to be movable into the path of the several laser beams 106,108, thereby enabling selective blocking of any selected one(s) of theseveral laser beams 106, 108 to selectively prevent formation of aportion of the optical traps 132. Such a methodology and structureenables construction of any desired array of the optical traps 132 byuse of appropriately designed knife edges or apertured knife edgestructure and like such structures.

[0062] An illustration of the use of such optical trap controlmethodology is shown in FIG. 9 wherein the optical traps 132 are formedby a holographic form of diffractive optical element 122. The movableknife edge 120 of FIG. 8 can block all but one line 124 of the opticaltraps 132. By systematically moving the knife edge 120, each of thelines 124 can be established, and this enables systematic filling of theoptical traps 132 with particles 126. This methodology allows filling ofthe optical traps 132 with a variety of different types of the particles126 and also avoids the typical problem of the particles 126 tending tofill preferentially the outer portions of an array of the optical traps132. Such preferential filling can therefore block filling of the inneroptical traps 132. This controlled formation of the optical traps 132also permits precision formation and change of optical traparrangements.

[0063] In addition to exerting detailed control over filling of an arrayof the optical traps 132, devices can be provided to accelerate fillingof the optical traps 132. For example, in FIG. 8 is shown a functionalblock 128 indicative of a device to (1) output selected particles 126(see FIG. 10), (2) apply the particles 126 under pressure differential(through electrophoresis or electro-osmosis), (3) apply a temperaturegradient and (4) translate the entire optical trap array through asuspension containing the particles 126 in a manner like a fishing net.Experimentation has determined the particles 134 can, for example, befilled into the optical traps 132 starting with a particle concentrationof about 10⁻⁴ μm⁻³ and a reasonable flow rate of about 100 μm/sec tofill one row of the line 124 or an array pattern in about one minute oftime. A fully developed array of the particles 126 can be made permanentby transferring the array onto a substrate or by gelling the fluid whichis suspending the particles 126. Such a procedure also can allowconstruction of a large variety of different particle arrays and coupledarrays of the particles 126. Using the previously-describedcharacteristics and functionalities of the optical traps 132, each ofthe particles 126 can also be further interrogated, imaged andmanipulated for operational uses and investigative purposes.

[0064] In yet another form of the invention the optical traps 132 can bedynamically changed responsive to a specific optical requirement. Theoptical requirement can be effected by use of a computer program withdesired instructional information such that one or more of the opticaltraps 132 can be used to modify, remove, or add particles at variousoptical trap sites or allow various manipulations of a single object.Further, one or more of the optical traps 132 can be moved and theircharacter changed (such as changing the shape or strength of the trap)for dynamic manipulation of any object, such as a cell of a plant oranimal. This can be particularly advantageous when manipulating adelicate structure or when there is need to perform complexmanipulations of an object. Heretofore, such objects were handles by asingle brute force trap which could cause damage to the object or notprovide the degrees of freedom often needed to perform a desiredfunction.

[0065] In addition, in another process the particles 126 can bedynamically sorted by size. One can also image an array of the particles126 in the manner shown in FIG. 10. A microscope 138 can image theparticles 126, and a personal computer 140 can identify the particles126 and calculate a phase only hologram 142 (for the diffractive opticalelement 144 of FIG. 8). To trap said particles, a computer controlledspatial light modulator 143 can then implement the computer designedhologram 142 by causing application of a pattern of phase modulations tothe laser beam 144. This can also be dynamically varied for any of avariety of purposes. The modified laser beam 148 (also see the severallaser beams 106, 108 in FIG. 8) are focused by the microscope 138 tocreate an array of the optical traps 132 (also known as tweezers) whichtraps the particles 126 for display on image screen 150. Each of theparticles 126 can then be individually manipulated to assemble a desiredstructure to sort the particles 126 or to otherwise manipulate, inspector alter the shape of the object of interest.

[0066] While preferred embodiments of the invention have been shown anddescribed, it will be clear to those skilled in the art that variouschanges and modifications can be made without departing from theinvention in its broader aspects as set forth in the claims providedhereinafter.

What is claimed is:
 1. An apparatus for manipulating particles,comprising: a diffractive optical element for receiving a light beam;and a focusing element downstream from said diffractive optical element.2. The apparatus as defined in claim 1 wherein said diffractive opticalelement is selected from the group consisting of an optical grating anda hologram.
 3. The apparatus as defined in claim 1 further including asystem for producing a laser beam for input to said diffractive opticalelement.
 4. The apparatus as defined in claim 1 wherein said focusingelement comprises at least one of an objective lens and a diffractiveoptical element.
 5. The apparatus as defined in claim 1 furtherincluding a telescope lens system disposed downstream from saiddiffractive optical element after interaction of the light beam withsaid diffractive element.
 6. The apparatus as defined in claim 5 whereinsaid diffractive optical element is disposed perpendicular to an opticalaxis of said telescope lens system.
 7. The apparatus as defined in claim5 wherein said diffractive optical element is disposed obliquely to anoptical axis of said telescope lens system.
 8. The apparatus as definedin claim 1 wherein said diffractive optical element creates a pluralityof diffracted output light beams.
 9. The apparatus as defined in claim 1wherein said diffractive optical element is disposed substantially in aplane conjugate to a back aperture of said objective lens element. 10.The apparatus as defined in claim 1 wherein said diffractive opticalelement is constructed to form optical traps at spatial locationsselected from the group consisting of positions in a focal plane and outof a focal plane formed by said objective lens element.
 11. Theapparatus as defined in claim 1 wherein said diffractive optical elementcomprises a dynamically changing diffractive component enablingdynamically changing optical traps to be formed by the apparatus. 12.The apparatus as defined in claim 11 wherein said dynamically changingdiffractive component comprises a computer-generated hologram.
 13. Theapparatus as defined in claim 12 wherein said apparatus further includesa liquid crystal component which is imprinted with thecomputer-generated hologram.
 14. The apparatus as defined in claim 5further including a mirror disposed for movement and positioned toreceive the light beam downstream from the telescope lens system. 15.The apparatus as defined in claim 1 further including means forperforming at least one of steering and focusing the optical trap. 16.The apparatus as defined in claim 15 wherein the means for performingcomprises a diffractive optical element.
 17. An apparatus formanipulating particles, comprising: a diffractive optical element forreceiving a laser beam; a first telescope lens system disposeddownstream from said diffractive optical element after interaction ofthe light beam with said diffractive element; and optical means forconverging the light beam output from said diffractive optical elementand said telescope lens system, thereby forming an optical trap.
 18. Theapparatus as defined in claim 17 further including a mirror disposed toenable movement of the optical trap.
 19. The apparatus as defined inclaim 17 wherein said mirror is mounted to enable translation of theoptical trap laterally and vertically.
 20. The apparatus as defined inclaim 18 further including a second telescope lens system disposeddownstream from said first telescope lens system and said mirror. 21.The apparatus as defined in claim 17 wherein said optical meanscomprises at least one of an objective lens and a diffractive opticalelement positioned to receive the light beam received from saidtelescope lens system.
 22. The apparatus as defined in claim 20 furtherincluding a beamsplitter disposed between said second telescope lenssystem and said optical means, thereby enabling viewing of images of theparticles being manipulated.
 23. A method for manipulating smalldielectric particles, comprising the steps of: generating a laser beam;inputting the laser beam to a diffractive element, passing thediffracted laser beam through a telescope lens system; and focusing thelaser beam output from the telescope lens system to form an optical trapfor manipulating the small dielectric particles.
 24. The method asdefined in claim 23 further including the step of steering the laserbeam using a mirror to thereby move the optical trap.